1. Field of the Invention
The present invention relates to an illuminating device for a display device (hereinafter, “display-device illuminating device”), and to a display device. More particularly, the present invention relates to a display-device illuminating device provided with a plurality of lamps that can be driven in parallel, and also relates to a display device.
2. Description of the Related Art
Common cold cathode lamps used as light sources for display devices have a non-linear negative impedance characteristic, and accordingly cannot be driven in parallel. Thus, each cold cathode lamp is generally provided with a separate power supply circuit. This configuration, however, is costly since it requires as many power supply circuits as there are cold cathode lamps, and also is disadvantageous in terms of size reduction, weight reduction, and cost reduction.
Moreover, common cold cathode lamps used as light sources for display devices are connected to power supply circuits via harness leads (also simply called leads) and connectors. Therefore, their fitting is troublesome, resulting in poor assembly efficiency with display-device illuminating devices employing cold cathode lamps; likewise their removal also is troublesome, resulting in poor replacement efficiency at the time of replacement of cold cathode lamps, and in poor disassembly efficiency at the time of discarding of display-device illuminating devices employing cold cathode lamps.
Known as lamps free from such disadvantages are external electrode fluorescent lamps (EEFLs) (see, e.g., JP-A-2004-31338 and JP-A-2004-39264), and the cold cathode lamps for which the present applicant applied for a patent (see WO 2006/051698 A1).
An external electrode fluorescent lamp is, in terms of an equivalent circuit, a serial circuit with a capacitor connected to each end of a negative resistance, and has a nonlinear positive impedance characteristic; external electrode fluorescent lamps can therefore be driven in parallel. On the other hand, a circuit comprising a cold cathode lamp disclosed in WO 2006/051698 A1, a first power feeding member, and a second power feeding member, wherein the cold cathode lamp is fed with electric power from a power supply device via the first and second power feeding members, is, in terms of an equivalent circuit, a serial circuit with a capacitor connected to at least one end of a negative resistance, and therefore has a nonlinear positive impedance characteristic; thus the cold cathode lamp disclosed in WO 2006/051698 A1 can be driven in parallel.
These lamps, as discussed above, can be driven in parallel, and can be fed with electric power via holders made out of a resilient metal member (e.g. spring steel), with the holders, under the resilience thereof, pinching and holding end portions of the lamps. This construction is advantageous in terms of easy fitting and removal of the lamps.
As shown in FIG. 8, in a display-device illuminating device employing such lamps as discussed above that can be driven in parallel, one end of each lamp 11 is held with a holder 12 provided on a first holding member 13, and the other end of each lamp 11 is held with a holder 14 provided on a second holding member 15. The lamps 11 are each supplied with an alternating-current voltage having a frequency of several tens of kilohertz from a power supply device 16 via the first holding member 13 and the second holding member 15. There are provided as many of each of the holders 12 and 14, which are made out of a resilient metal member (e.g. spring steel) as there are lamps. An A-A′ section of the second holding member 15 shown in FIG. 8 is as shown in FIG. 9A, and a B-B′ section of the second holding member 15 shown in FIG. 8 is as shown in FIG. 9B. Note that the shape of the first holding member 13 is similar to that of the second holding member 15.
In the configuration shown in FIG. 8, as in other known art (e.g., see JP-A-2003-36723), a connecting point of the first holding member 13 and a harness lead 17, which is connected to one end of a power supply device 16, is provided at a bottom end portion of the first holding member 13, and a connecting point of the second holding member 15 and a harness lead 18, which is connected to the other end of the power supply device 16, is provided at a bottom end part of the second holding member 15. Therefore, the influence of a voltage drop resulting from an ohmic loss is greater the closer a lamp is located to the top of the first holding member 13 and the second holding member 15; thus the closer a lamp is located to the top of the first holding member 13 and the second holding member 15, the smaller the lamp current therethrough. This results in uneven brightness.